The quality of sound in terms of duration and level is not satisfactory in the high register of the piano, and unlike the other registers, dampers are not necessary. This problem is related, mainly, to the coupling between the strings, the bridge, and the soundboard. To enhance the tonal quality of this register, some piano makers add extra sound produced by the oscillation of the short rear section of strings, properly tuned (octave, fifth or unison) in line with the vibrating section and driven by the latter through the bridge (this is called ”duplex scale”). To analyze the effect of the ”duplex scale”, experimental and theoretical studies were carried out on a real piano and on an individual sample of a Grand Piano built by the Tallinn Piano Factory for A. Stulov of the Institute of Cybernetics, specially prepared for experimental measurements. Inspired by the model of nonconservately coupled oscillators of G. Weinreich (J. Acoust. Soc. Am. 62, N 6, 1977), extended to a third oscillator, we investigate the energy transmission between the string coupled through the bridge and analyze the effect of the ”duplex scale” in the high register. Results will be presented and discussed. [Support from Egide-Parrot program, project N 82/239584, is acknowledged].